The aim of the current study was to investigate the impact of classroom-based physically active brain-breaks on the in-school activity levels of Grade 1 (six- to eight-years-old) learners (N = 48) by comparing baseline results to the intervention PA patterns of the participants. Children wore Actigraphs accelerometers for five consecutive school days, and thereafter they participated in a six-week active brain-breaks (10-minute bouts of PA) intervention. On a typical school day, children spend an average of 106.2 ± 30.9 minutes in sedentary behaviour, 43.7 ± 13.7 minutes in moderate PA and 26.5 ± 13.6 minutes in vigorous PA. No differences were found between boys and girls. During the intervention, the children's sedentary behaviour decreased (100.1 minutes) and their vigorous PA increased (34 minutes). The results emphasise the importance of participation in daily FMS and PA in order to increase Grade 1s' in-school PA patterns and decrease sedentary behaviour.